The present invention concerns a metal tear-off cap which acts as a pressure closure means and can be secured by crimping on to the neck of a containerx (1) FNT (1), the cap having a tear-off strip extending around the cap surface, bounded by at least one tear line of reduced strenth, a portion of the tear-off strip being covered by a foil.
Among the requirements for an ideal pressure closure means are that it should provide a good seal and it should be capable of ready removal without the use of a tool or implement. The closure means desirably should show whether the original contents of the bottle have been tampered with, and it must be hygienic and have no adverse effect at all upon the contents of the bottle. However, many existing pressure closure means fail to meet all the above requirements. Thus, for example, the known screw-on caps do not guarantee that the original contents of the container have not been interfered with, and crowned caps cannot be removed without the use of an implement.
There are existing metal tear-off caps for sealing bottles and other containers, which have a tear-off strip, a portion of the tear-off strip being covered by a foil or film. German Pat. No. 1,204,544, for example, describes a tear-off cap, part of the tear-off strip of which is formed to provide a holding tab by means of a perforation of the cap skirt, the perforation for said holding tab being covered by a foil also extending around the latter, which foil may project over the free end of said holding tab and can be secured to the holding tab through openings.
This and other tear-off caps with a tear-off strip and a punched-out holding tab - with and without covering foil - which are to be secured on to the neck of a container by crimping, have the disadvantage that they cannot be used as pressure closure means since the skirt surface of the cap is radially perforated along the length of the holding tab. If after closing a container by means of such a tear-off cap, an axial pressure is exerted upon the cap from inside by the contents the skirt surface normally compressed onto the neck of a container arches upwardly above the longer radial perforation despite the crimping; and the seal is destroyed.
Furthermore, the holding tabs produced by punching operations have the disadvantage that a hardening of the material occurs all around the cut edges. Such a hardening interferes with the functioning of the holding tab at the two points where the holding tab ends and the tear-off strip starts. The undesirable initial resistance which occurs when pulling off the tear-off strip greatly hinders opening of the container. An even greater disadvantage are tears in undesired directions produced as a result of the hardening, which prevent the proper functioning of the cap.
A further disadvantage of the known tear-off cap is that in their production a sensitive punching tool is required for punching out the holding tab. Since the holding tab is connected with the tear-off strip only at one narrow side for securing the foil or film the other three sides are free, there must be a tongue of appropriate shape in the matrix of an appropriate punching tool. This free narrow tongue of the tool is extremely sensitive to shock and pressure and therefore not well suited for robust mechanical production with several hundreds of punchings per minute.
This tool construction causes the further disadvantage that for the tear-off strip one must not exceed a minimum height required to fasten the free tongue in the matrix. Thus, the shape of the holding tab necessarily determines the height of the tear-off strip and therefore influences the total height of the cap. For this reason, the tear-off strip cannot be formed in a narrower size, which would make it possible to reduce the height of the cap. In the production of an enormously large number of caps, even a small reduction in height would afford a very large saving of material and cost.
In addition, the long radial perforation of the cap skirt interferes with the smooth passage of the cap through the feed mechanism and the machine. The cap skirt, which has reduced strength due to the perforation for the holding tab, tends to be dented at the high transport rates in the sorting and conveying systems, which damage the caps and interfere with their transportation.
The invention is directed to the object of providing simple and economical metal tear-off cap having a tear-off strip and foil on one portion of the tear-off band to be secured on to the neck of a container by crimping, which cap is useful as pressure closure means and meets all the above requirements to be met by a pressure closure means.